Ever since R600 samples were handed out by AMD, people have been asking me for R600 support in ATITool. It's coming along nicely, but is not quite ready yet.
In the meantime you can use this nifty little tool from AMD. It can change 2D/3D clocks and lets you monitor temperatures of the card. It also works on RV610, RV630 and all previous products like the R5xx Series. It works under 2k, XP, Vista, 32-bit & 64-bit.